1. Field of the Invention
This invention relates generally to the making of abrasive articles and the like, and is more particularly concerned with the use of soft, flexible and easily deformable powdered pieces as preforms for the manufacture of abrasive articles having abrasive particles therein.
2. Discussion of the Prior Art
Powdered preforms are widely used in the manufacture of abrasive articles that include a plurality of abrasive particles such as diamond, cubic boron nitride and the like. Such powdered preforms are conventionally manufactured by compacting powder mixtures of retaining compositions and superabrasives particles in cold presses or roll compactors to form green compacts. Compacting pressure ranges from 300 to 10,000 kg/sq. cm, resulting in 20-50% relative density of the green compacts. Such green compacts are hard, stiff and brittle. The green compacts are then sintered, either with or without pressure, and with or without impregnation.
There is a method of making abrasive articles wherein a non-compacted mixture of the powdered retaining composition, with a plurality of abrasive particles therein, is placed directly into a sinter mold, then compacted and sintered in the sinter mold. This method requires a lot of adjustments in attempts to spread the powder evenly within the sinter mold. The required adjustments slow the manufacturing process, so the method does not fit well with mass production requirements.
In all the above mentioned methods, the powdered mixture can contain some binders, but the conventional green compacts are held together, not by the binder, but primarily by interaction among the particles of the powder, e.g. by mechanical interlocking of the particles. The above mentioned methods are widely used to produce traditional cutting, drilling, and grinding abrasive tools and elements of abrasive tool, such as segments for saws and the like.
There are powdered preforms formed by spraying powder onto a substrate, and fixing the powder to itself and to the substrate by an adhesive, for example by an adhesive spray. Such preforms are flexible, but may experience loss of some powder when flexed. Also, such a method must deal with air borne particles and aerosol sprays that, because of environmental concerns, put serious limitations on the implementation of the method. This method has been used by the present inventor to make articles disclosed in U.S. Pat. Nos. 4,925,457, 5,049,165, 5,092,910 and 5,190,568, as well as in U.S. patent application Ser. No. 08/066,475 titled "Patterned Abrasive Material and Method", and U.S. patent application Ser. No. 08/024,649 titled "Abrasive Cutting Tool".
Soft and flexible preforms of powders and/or fibers, including both metallic and non-metallic materials, are also known; but, to the knowledge of the present inventor, such preforms are not known in the art of manufacturing articles that include abrasive particles. Presently, the soft and flexible preforms are made by casting, or extruding a composition of brazing filler metal, or ceramic components, or hard facing compositions including metallic components and non-metallic components such as tungsten carbide particles. Such soft and flexible preforms can be bent more than 90.degree., and can be cut by scissors or the like.
The earlier known soft and flexible preforms comprise a high content of various binders, up to 95% by volume, and up to 20% by weight. It is the binder that makes such preforms soft and flexible; but, even with the high content of binders, the preforms are flimsy and must be handled with care. This is especially true for the very thin preforms, around 0.005-0.010", or 0.10-0.25 mm.
It is important to distinguish between the soft and flexible preforms and the products of roll compacting of powders, even in the presence of a binder. When a roll compacted product includes a binder, the binder is in a much smaller quantity than in a flexible preform. The roll compacted product is held together, not by the binder, but by the mechanical interlocking of particles, which makes the roll compacted product much less flexible than the soft and flexible preforms.
Soft and flexible preforms made of brazing filler metal compositions are used to put some parts together through brazing, mostly through furnace brazing. Soft and flexible preforms made for hard facing compositions are used to repair worn parts. For this purpose, the preforms are applied to a worn spot on the part.
The brazing process using the soft and flexible preforms made of brazing filler metal has a significant time duration because of the necessity for removal of the substantial quantity of binder. The time for removal of the binder is called the "dewaxing" cycle, and it allows the binder to melt, evaporate, or run out from the preform. It has been found that, if the dewaxing time is shortened or omitted, the powder of the soft and flexible preform can be literally washed out by the liquefied binder.
In attempting to use the known soft and flexible preforms to hold a plurality of abrasive particles in order to produce abrasive articles, it will be recognized that:
1. Compositions of the brazing filler preform do not correspond to the desired matrix compositions to hold abrasive particles; PA0 2. Soft and flexible preforms are not produced with abrasive particles on, or within, the preforms; PA0 3. Soft and flexible preforms are quite flimsy and not as strong as desired for production of abrasive articles, especially for mass production requirements of abrasive articles requiring thin (0.005-0.020", or 0.1-0.5 mm) flexible preforms; PA0 4. De-waxing time must be severely reduced to meet production rates, especially for mass production; and, PA0 5. Heating and/or brazing processes alone do not provide the most reliable matrix for retaining abrasive particles.